Does nature hold the answer to flooding?


Wednesday, May 09, 2018

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Heavy rains over the past few days have resulted in flooding events in various sections of the island. They bring to mind several events in 2017, the most significant of which was perhaps the November 22nd flooding in Montego Bay, in which just four hours of intense rainfall wreaked havoc in the downtown city centre. To say that these events are destructive and result in millions of dollars in losses, repairs and clean-up, would be to understate the facts. Not to mention the substantial risk to life and health.

As such, both the State and citizens should put into practice any action that can be taken to reduce the risk and severity of flooding. Proper disposal of garbage is always a good move, but here a few others that we should consider.

WetlandS Conservation

Wetlands refer to any area which is periodically saturated with water. They can be coastal, as in mangroves and brackish marshes, or located further inland, such as swamps and peat bogs. They provide many important ecological roles to the surrounding environment, including protection and improvement of water quality, provision for fish and wildlife habitat and shoreline protection. What is less known, however, is that wetlands are important systems for flood control. They act as water detention or flood storage areas and in so doing, reduce peak flood flows. Some major wetlands in Jamaica include the Great Morass in St Thomas and the Black River Morass in St Elizabeth. It is crucial that these areas be protected, not only for the critical ecological roles that they play, but also for their role in reducing flooding. The protection and conservation of wetlands falls under the mandate of the National Environment and Planning Agency. However, citizens can do their part to maintain the integrity of these systems by not littering, not filling in the areas with earth, and not removing trees or other assets.

Sediment Control

All watercourses have a finite carrying capacity. If there are too many solids being transported by the water in a watercourse or drainage system, the system will be overwhelmed and spillage, or overtopping of the system, will occur. This is particularly relevant when the watercourse constricts, such as at a culvert or bridge. The solids (whether sediment, debris or garbage) will pile up at these structures and impede the flow of water.

Construction activities are some of the biggest culprits in regard to sediment loading in watercourse or drainage systems. To prevent the occurrence, it is imperative that any exposed soil and/or rocks on construction sites be secured. The application of a soil stabiliser (for example, wood mulch) to bare soil surfaces is an example of an effective measure to protect the soil from water and wind erosion. A silt fence (if properly installed and maintained) is also an excellent measure to put into place. Lastly, it is critical that the inlets of storm drains collecting runoff from the construction sites are protected.

Decrease Deforestation

Deforestation is also a culprit in regard to sediment loading in watercourses. Removal of trees decreases the structural support given to the soil by fine roots. The intertwining of root systems between trees forms a network that holds soil in place. As a tree is cut, roots begin to decay and the reinforcement to soil strength they offer is quickly lost. The removal of the vegetation therefore leads to increased soil erosion and movement. Another consequence of the deforestation process is that unwanted logs or tree trunks are left lying on the ground. These will also wash down into the watercourses, causing severe blockage in many instances.

It is therefore important to safeguard forested and vegetated areas as much as possible. Community initiatives to reforest upper sections of watersheds can play a key part in reducing sediment loads that report to the watercourses.

Johanna Richards is a water resources engineer at Water Resources Authority.


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